Continuity mistake: The character Will is holding a rifle that has a carrying handle on top. Then, as the three characters walk away, the rifle he is holding has a flat top with no sights. In the next scene, his rifle has a carrying handle. (00:26:45 - 00:27:45)
Factual error: The physicist is on a quest for magnesium oxide, but it's one of the easiest things to obtain; magnesium is used in some engines, alloy wheels, and the humble block of magnesium used in camping fire starters. One could simply cut a ribbon of it, set it alight, and voila! Magnesium oxide.
Factual error: After three years, the lights on the mining helmets are still working. The batteries would have corroded or discharged by then.
Suggested correction: Non-rechargeable lithiums and certain rechargeable batteries have a shelf life of years while retaining sufficient charge.
Factual error: The scientist's car wouldn't still be able to start after standing in the lab's parking lot for three years.
Other mistake: It is three years since the Reapers emerged, but when they reach the Ranger Station, the pick-up truck is still spotlessly clean, and the tyres are still inflated.
Plot hole: In the end, the scientist makes a bullet that can destroy the Reapers. She shoots one inside her lab with the Reaper a very short distance away from her, and the scene cuts. A little later, she shoots a Reaper outside, which results in a violent explosion. An explosion that size would have most likely killed her and destroyed the entire floor, plus the floor above and below the lab. However, when she shows up, she is not injured or burned.
